1. Field of the Invention
The present invention relates to a TV signal receiving tuner and, more specifically, to a TV signal receiving tuner which can be reduced in size and cost.
2. Description of the Related Art
TV signals are divided into UHF (806 to 470 MHz in the U.S.), VHF high-band (216 to 174 MHz in the U.S.) and VHF low-band (88 to 54 MHz in the U.S.) signals when they are received.
As shown in FIG. 3, a tuner comprises an input terminal 32 connected to an antenna 31, a UHF mono-tuning circuit 33, a UHF high-frequency amplifier 34, a UHF multi-tuning circuit 35, a UHF mixer 36, a UHF local oscillator 37, a UHF resonance circuit 38, a VHF high-band mono-tuning circuit 39, a VHF high-band high-frequency amplifier 40, a VHF high-band multi-tuning circuit 41, a VHF high-band mixer 42, a VHF high-band local oscillator 43, a VHF high-band resonance circuit 44, a VHF low-band mono-tuning circuit 45, a VHF low-band high-frequency amplifier 46, a VHF low-band multi-tuning circuit 47, a VHF low-band mixer 48, a VHF low-band local oscillator 49, a VHF low-band resonance circuit 50, a filter 51, an intermediate-frequency amplifier 52, a PLL IC 53, a quartz oscillator 54, a local oscillator switch 55 and a tuner output terminal 56.
To receive a UHF TV signal, a TV signal received by the antenna 31 is tuned by the UHF mono-tuning circuit 33, amplified by the UHF high-frequency amplifier 34, and tuned by the UHF multi-tuning circuit 35. The tuning frequencies of the UHF mono-tuning circuit 33 and the UHF multi-tuning circuit 35 are changed by a tuning voltage Vt output from the PLL IC 53 and tuned at the frequency band of a channel to be received. Since the output impedance of the antenna 31 is low and the input impedances of the UHF high-frequency amplifier 34 and the UHF multi-tuning circuit 35 are high, impedance matching is carried out by the UHF mono-tuning circuit 33.
The TV signal output from the UHF multi-tuning circuit 35 is applied to the UHF mixer 36. One input terminal of the UHF mixer 36 is connected to the output terminal of the UHF multi-tuning circuit 35 and the other input terminal is connected to the UHF local oscillator 37. The UHF local oscillator 37 is connected to the UHF resonance circuit 38 so that a local oscillation signal output from the UHF local oscillator 37 is changed by the tuning voltage Vt input from the PLL IC 53 into the UHF resonance circuit 38. Since the UHF local oscillator 37 outputs a local oscillation signal which is 44 MHz higher than a TV signal to be received, a converted signal having an intermediate frequency of 44 MHz is output from the output terminal of the UHF mixer 36.
The intermediate-frequency signal is applied to the filter 51. The filter 51 is a band-pass filter having sharp characteristics and connected to the intermediate-frequency amplifier 52. The intermediate-frequency signal amplified by the intermediate-frequency amplifier 52 is output from the output terminal 56 of the tuner.
When a VHF high-band TV signal is received, the TV signal received by the antenna 31 is applied to the filter 51 through the VHF high-band mono-tuning circuit 39, VHF high-band high-frequency amplifier 40, VHF high-band multi-tuning circuit 41 and VHF high-band mixer 42. As the operations of the above circuits are the same as the UHF circuits, their descriptions are omitted. As the operation of the VHF high-band local oscillator 43 and the operation of the VHF high-band resonance circuit 44 are also the same as the UHF circuits, their descriptions are omitted.
When a VHF low-band TV signal is received, the TV signal received by the antenna 31 is applied to the filter 51 through the VHF low-band mono-tuning circuit 45, VHF low-band high-frequency amplifier 46, VHF low-band multi-tuning circuit 47 and VHF low-band mixer 48. As the operations of the above circuits are the same as the UHF circuits, their descriptions are omitted. As the operation of the VHF low-band local oscillator 49 and the operation of the VHF low-band resonance circuit 50 are also the same as the UHF circuits, their descriptions are omitted.
The PLL IC 53 is a circuit for selecting a channel to be received. To receive a UHF band channel, a UHF band switch voltage Vu for selecting a UHF band channel is applied to the UHF high-frequency amplifier 34 and a tuning voltage Vt corresponding to the selected channel is applied to the UHF mono-tuning circuit 33, the UHF multi-tuning circuit 35 and the UHF resonance circuit 38. To receive a VHF high-band channel, a VHF high-band switch voltage Vhi for selecting a VHF high-band channel is applied to the VHF high-band high-frequency amplifier 40 and a tuning voltage Vt corresponding to the selected channel is applied to the VHF high-band mono-tuning circuit 39, the VHF high-band multi-tuning circuit 41 and the VHF high-band resonance circuit 44. To receive a VHF low-band channel, a VHF low-band switch voltage Vhi for selecting a VHF low-band channel is applied to the VHF low-band high-frequency amplifier 46 and a tuning voltage Vt corresponding to the selected channel is applied to the VHF low-band mono-tuning circuit 45, the VHF low-band multi-tuning circuit 47 and the VHF low-band resonance circuit 50. Further, a control voltage is applied to a local oscillator switch 55 in the PLL IC 53.